Subtitles disappear when seeking backward on certain streams.

[HugoSaintLaurent]

Environment

• The MPD passes the DASH-IF Conformance Tool on https://conformance.dashif.org/
• The stream has correct Access-Control-Allow-Origin headers (CORS)
• There are no network errors such as 404s in the browser console when trying to play the stream
• The issue observed is not mentioned on https://github.com/Dash-Industry-Forum/dash.js/wiki/FAQ
• The issue occurs in the latest reference client on http://reference.dashif.org/dash.js/ and not just on my page

• Link to playable MPD file: https://livesim2.dashif.org/vod/testpic_2s/multi_subs.mpd
• Dash.js version: 4.7.4/5.0.0
• Browser name/version: Google Chrome 125.0.6422.142
• OS name/version: Windows 10

Steps to reproduce

It can be reproduce in dash reference player as follow:

1. Uncheck the loop check box in the options.
2. Select Stream -> Subtitles and Caption -> [DASH-IF]TTML Segmented Subtitles VoD
3. Press Load
4. Let the stream play for a 1 or 2 minutes.
5. Then seek back at the beginning of the stream.
   You will notice that captions previously displayed at the beginning of the stream are now missing and no longer displayed anymore because they have been removed from the text track cue list. And there corresponding vtt boxes/text fragments ( https://livesim2.dashif.org/vod/testpic_2s/sub_eng/24.m4s for example) haven't been reloaded.

Captions will reappear when you reach a point where they are still present in the cue list of the text track.

Another way to reproduce this issue is to play the stream until them end, and press play again.

Observed behavior

Calling _deleteOutdatedTrackCues() in TextTrack.js's addCaptions() is causing issues when seeking or starting over (Seeking to 0) when text fragments are scattered throughtout the stream. Once outdated cues are deleted, they are not redownloaded when the user seek back to a position in time where deleted text cues were, resulting in the disappearance of the captions for that time.

Expected behavior

Redownload the captions, or only delete outdated captions when they are out of the seekable range.

[HugoSaintLaurent]

Console Logs:
Subtiltes missing log.txt